Process of making mono-ammonium phosphate.



V F. S. WASHBURN.

PROCESS "OF MAKING MON0AMMON|UM PHOSPHATE.

APPLICATION FILED AUG-3, 1914.

" 1,142,068. Patented June 8, 1915.

FRANK S. WASHBURN, 0F NASHVILLE, TENNESSEE.

PROCESS OF MAKING MONO-AMMONIUM PHOSPHATE.

Specification of Letters Patent.

Patented June 8, 1915.

Application and August s 19 Serial in). 854,855.

To all whom it may concern;

a citizen of the United States, residing at Nashville, in the county of Davidson and State of Tennessee, have invented certain new and useful Improvements in Processes of Making Mono-Ammonium Phosphate; and I-do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of making ammonium phosphate especially adapted for fertilizer purposes from phosphate rock, and has for its object to provide a process which will be more eflicient and less costly than those heretofore proposed.

With these and other objects in view the invention consists in the novel steps and combinations of steps constituting my 1nvention, all as will be more fully herein-' after disclosed and particularly pointed out in the claims.

Referring to the accompanying drawing forming a part of this specification in which the figure is a diagrammatic illustrafor steam from said system. H I

5 indicates an acidcirculating pump con 'tion of-one form of apparatus suitable for carrying out my process, 1 indicates suitable dissolvmg tanks for treating finely d1? vided phosphate rock with sulfuric acid; 2

a filter press. for separating the phosphoric acid solution from the. insoluble residue; 3 a discharge vpipe from the filter press 2 into the acid heating tankfor} system 6; and i represents any suitable'esc'ape pipe nected to the acid heating system 6 as shown; and 11 a pipe for conducting hot acid to the first ammoniating tower 9, while 10 represents a pipe conducting unabsorbed ammonia vapor and gases to a second ammoniating tower 8 connected to the acid heating system 6 by the steam conducting pip 13 represents an inlet for a mixture of' steam and ammonia fed to the first tower 9; and12 a pipe connecting the fresh acid tank 25 with the adjusting tank 14 adapted to receive super ammoniated acid from tower 9. a

15, 16 and .17 represent a tripleefiectevaporator the elements being connected as feet 17 the pipe 26 and to the efiect 15 by the pipe 27 as illustrated.

l9 and 20 represent alternate receivers for the fused liquid under a high vacuum, while 21 represents a surface condenser and 22 a vacuum pump connected as'shown.

In order that my process may be clearly understood it is said: I start with finely ground phosphate rock in tanks 1, and add sufiiclent-sulfuric acid to the same to convert all of the tri-calcium phosphate into calcium sulfate and free phosphoric acid, and dissolve the impurities in the rock, by adding an additional amount of sulfuric. acid. If it is desired to produce this phosphoric acid in a dilute form, the quantity of sulfuric acid to be added need only be sufaction, which is found to play an increasingly important part in the reaction as. the concentration of phosphoric acid in the solutions increases. or instance, if one wishes to obtain a 2Q%. P 0 solution, it is necessary to have in this solutions few tenths of a per cent. of free sulfurlc acid in order to obtain a high efliciency of extraction, while .if one wishes ,to'work to as high as 25% P O 'in the extracted phosphoric acid, then this solution should contain nearly 1% "of tion'of phosphoric acid from the rock. 1

next separate this solution "of phosphoric acid from the calcium sulfate and other impurities by filtration, asbypassing it through the filter press 2, and washing it; and, I thereby obtain a clear solution of crude phosphoric acid containing only a few tenths of a per cent. of such impurities free sulfuric acid toobtain a high extra'ci as iron, alumina and soluble lime, with a slight amount of free sulfuric acid, as above explained.- This said clear solution is led from the filter 2 by means of the pipe ,3. to the tank, or heating system6. I may ammoniatev this crude solution of phosphoric acid in any suitable manner, such as by adding aqua ammonia thereto, or by passing ammonia gas into the same.= But I prefer to use the ammonia vapor made from use merely as a vwaslgiing'tower'for clearing I 60 phoric acid.

commercial calcium cyanamid or lime nitrogen, which contains large quantities of steam, at a high temperature. To accomplish this I fill the towers Sand 9'W1th 5 chemical brick, and feed the crude phoswhile from the'top of said tank 8 thepipe 7 leads anyunabsorbed gases, or vapors, into the acid heating system or.- tank 6, to warm up the, acid solution befo e it reaches tank 9.- In the first tower 9 fed with the ammonia,

I so regulate the phosphoric acid, that when it leaves at the bottom, it istransformed into a mixture of mono-ammonium and di-ammonium phosphates, with as much of the latter as I can possibly obtain in'other Words, in this tower I have a fairly large excess of ammonia. Into the second tower 8', which I up the ammonia escaped from the first tower, I pass through the pipe 23. a large excess of-phosphoric acid, so .as to be certain 'to entrap all the lasttraces of ammonia. In this way I condense nosteam in the system, allow no ammonia to escape unabsorbed, and at the same time make an ammonium phose phatesolution quite high in di-ammomum 8-6 phosphate. ,Th'ls ammonium phosphate solution Ithenrrun into the adjusting tank, 14, through the pipe 31, and then add suflicient phosphoric acid to exactly neutralize it to the mono-ammonium phosphate stage. 7

The process of neutralization of this solut on I have found involves some complications inasmuch as methyl *orange the usual indicator, which has always been used for this work, does not indicate exact neutrality,

but possesses a lag in its, indications; so that if one were to operate without corrections, one would not obtain a strictly neutral solut1on of mono ammonium phosphate, but would obtain a solution of mono-ammonium phosphate containing about one fourth, of

1%. of the phosphoric acid in the di-am monium form. In ,the subsequent treatment ofthe product by this process, I have found.

that di-ammonium phosphate is decomposed into monq-ammonium phosphate, with a consequent loss of ammon1a;-and, therefore,1n,

order to avoid this loss I find it necessary to correct for this lagof the indicator, by

adding a corresponding quantity. of phosam aware of'thefact that there are existing patents calling for the neutralization of phosphoric acid by the 'use of ammonia,

either in excess or .to alkalinity, ,But such 36 neutralizedsolutions, if treated in the manner. hereinafter described, I have found al- Ways lose ammonia, and I, therefore, find it necessary to work in the manner just described, if one desires to avoid suclrlosses.

I have also discoveredthat such a solution of mono-ammonium phosphate possesses rather pecullar propertles in regard to" 1ts temperature concentration phenomena. That is to say, starting with a boiling point of something over (1, depending upon the initial concentration of the phosphoric acid, and which for a 20%, P 0 solution is approximately 102 0., the boilingpoint slowly rises with an increase in concentration to 105 C. From this point on, the rise ismuch more rapid with an increase of the concenv tration than it has been up to the said point, until a temperature of 112 C. is reached, at which temperature, if the material is cooled, it will set to a solid mass, 'though it is .still quite liquid when the'temperature of 112 C. is first reached. Itherefore-conclude that what happens 'is the following: The rise in temperature from 102 C. up to 105 C. is, probably, simply a concentration ofthe solution; but from 105 there is probably a true fusion of the separated salt in a satu-" rated solution ofammonium phosphate, up to a temperature of1f12 0., at which point the rest of the water is simplyidriven off without arise in temperature. At 112 C. the fused mass contains approximately 10% of-water; If heating is continued this water is lost andthe material will set in the evaporating apparatus to a solid mass, which cannot be removed except by a most laborious means. But if this material is tapped out of the evaporator at.112 C. into a very highly evacuated receiver, the sensible/heat in the fused mass is sufficient to evaporate off nearly all of the water the instant the mass 1 is discharged into the high vacuum, and one .thus obtains directly from such receiver a product containing only 3% or 4% of water, and in a granulated form, which practically needs no othcr dryingx A convenient way of carrying out the above process of evaporation involves, therefore, the following steps :I provide a multiple effect evaporator 15, 16, 17 and into the second effect 16 I pump through the pipe 30, the solution of ammonium phosphate from the adjusting tank 14, carrying it as usual to the last effect of my system through the pipe 29 and pump it back into the first eifect 15 through; the plpes 26 and 27 which effect .15 I supplywith steam at such pressure, by

means not shown, that I can'readily obtain a final temperature of'the liquid in this said effect 15 of 112 C. or thereabouts.

thus obtain in said efiect l5 by this system of evaporation a fused product under atmospheric or superyatmospheric pressure; and which product I alternately tap out by means of a suitable yalve into eration I have avoided the very great difiiculty of drying a highly concentrated and wet solution of ammonium phosphate, such as would be'obtained if ordinary evaporators were used. A product obtained from such ordinary evaporators would be'so wet and adhere .so strongly to iron that it would be impossible to dry it through any of the within ordinary direct fired types of driers the limits of reasonable costs.

What I claim is:

1. The process of making mono-ammonium phosphaite, substantially devoid of diammonium phosphate from a solution of phosphoric acid which consists in feeding ammonia to said solution and testing the latter with a chemical indicator; and overcoming the lag of said indicator by so proportioning the quantities of acid and ammonia that said indicator will show a slight acid reaction, substantially as described.

' 2. The process of preventingthe presence of substantial quantities of di-ammonium phosphate in the manufacture of mono-ammonium phosphate from a solution of phosphorica'cid, which consists in treating said solution with ammonia until a chemical indicator shows a slight alkaline reaction;

and then adding additional acid to an amount less than one per cent, substantially as described. a

3. The process of making mono-ammonium phosphate substantially free from di-ammonium phosphate from phosphate rock and ammonia which consists in treat- 4. The process. of making mono-a mmonium phosphate substantially free from di-ammonium phosphate from phosphate rock and ammonia, which consists in treating said rock with sulfuric acid to form a crude solution of phosphoric acid; suitably filtering said solution; treating said crude filtered solution with ammonia until achemical indicator shows a sli ht alkaline reaction; and then adding su cient phosphoric acid to overcome the lag of said indicator and to cause the latter to show'a slight acid reaction, substantially as described.

5. The process of making mono-am-v monium phosphate substantially 'free from di-ammonium phosphate from phosphate rock and ammonia which consists in treating said rock with suflieient sulfuric acid to liberate the phosphoric acid and to dissolve the impurities present, thereby form .ing a crude solution of phosphoric acid;

filtering said crude solution; treating said crude filtered solution with ammonia untila chemical indicator shows a slight alkaline reaction; and then adding suiiicient phosphoric acid to overcome the lag of said in-- dicator and to cause the latter to show a slight acid reaction, substantially as de- K scribed. p

6. The process of making a crude solution of phosphoric acid of a predetermined strength from phosphate rock, which consists in finely dividing said rock; adding thereto suflicient sulfuric acid to liberate the phosphoric acid present; adding-an additional amount of sulfuric acid to dissolve the impurities in the rock; and adding a further quantity of sulfuric acid in accordance with the law of mass action and according tothe concentration'of phosphoric acid desired, substantially as described.

7. The process of making afmono-ammonium solution from phosphate rock, which consists in finely dividing said rock; adding thereto suflicient sulfuric acid to liberate the phosphoric acid present; adding an additional-amount of sulfuric acid to dissolve the impurities in the rock; adding a further quantity. of sulfuric acid in accordance. with the law of mass action and according to the concentration of phosphoric acid desired; subjecting said solution to the action'of a suitable filter and suitably treating said solution with ammonia; substantially as described.

In testimony whereof I aflix my signa-' ture, in presence of two witnesses.

FRANK S. WASHBURN. Witnesses:

A. E. BENN, G. SCHURMAN. 

